On a reverb send, keep MIX at 100 % and put a whole group in one shared space — automate BREATH up in a breakdown to make the room swell.
What NEBULA is
NEBULA is a large-scale FDN reverb that doesn't try to copy a room — it builds spaces that don't exist and then lets them breathe. A feedback delay network with a Householder mixing matrix gives you dense, smooth tails up to a few seconds long, and a perceptual layer reduces the whole thing to five honest macros. The signature move is the breath: a 3-sine LFO of its own modulates the space so the tail is never perfectly still — it inhales and exhales without sounding like cheap chorus.
Where it shines It shines on pads, vocals, guitars and synths that need to sit inside a space, on sustained sources you want to hold and swell, and on send buses where a whole group should share one room. It does cathedral and infinite-freeze territory just as easily as a tight, dark ambience — and it stays mono-safe.
Up and running in five steps
- Drop NEBULA on a track, or on a send/aux bus to put a whole group in the same space (lower MIX for a track, keep it high on a send).
- Set SIZE to scale the room — small ambience down low, a vast hall up high — and DECAY for how long the tail rings out.
- Pull TONE up to darken the tail (treble decays first, like a real room) and shape its color.
- Bring BREATH up until the space starts to move — 20–40 % is alive but subtle; leave SYNC off for an organic drift or turn it on to lock the breathing to your tempo.
- Blend with MIX, then drag the CLOUD field directly (← SIZE, ↕ DECAY) to dial it in by feel.
How the signal moves through it
The dry signal feeds a feedback delay network: N mutually-prime delay lines recirculate through a lossless Householder mixing matrix for maximum density, with no metallic ringing. DECAY sets the per-line feedback gains (T60) — at the top it clamps right at the edge of unity for an infinite, frozen tail — while a damping filter inside each line shapes a frequency-dependent T60 so highs fade before lows, driven by TONE. SIZE scales the delay lengths to grow or shrink the space, and a slow breath modulator (a 3-sine LFO of its own) continuously nudges those lengths and character by the amount of BREATH, syncable to host tempo. Finally a shared LOW CUT / HI CUT pair filters the full plugin output (dry + wet, so the cut is audible at any MIX), a true-peak limiter with 3 ms lookahead keeps it clip-safe, and MIX cross-fades wet against dry with an equal-power law.
Every control, explained
CLOUD
The big breathing field — NEBULA's visual heart and an XY macro.
Drag horizontally to set SIZE and vertically to set DECAY. The cloud expands and contracts with the breath, its density tracks DECAY and its color tracks TONE. Reads out density, RT60, size, breath and tint live.
Use it for fast, by-ear setup: throw the cloud big and dense, then fine-tune the macros with the knobs.
SIZE
The scale of the space.
0–100 % (default 50). Scales the FDN delay lengths from a small room up to a vast ~2 s space; the gains recompute so DECAY stays put as you resize.
Big SIZE with low DECAY gives a short but wide ambience; small SIZE with high DECAY gets dense and resonant.
DECAY
How long the tail rings out (T60).
0–100 % (default 50). Sets the feedback gain per line; multiplicative in dB with a floor so it fades to silence cleanly. At the top it clamps at the edge of unity for an infinite, frozen tail.
Push DECAY to 100 % for a freeze pad you can play over; back off to ~60 % for a long-but-musical hall.
TONE
Damping — the color of the tail.
0–100 % (default 40). Sets the absorption filters inside each delay line so the high end decays faster than the low end, like a real room. Higher = darker, more absorbed tail.
Raise TONE on bright sources so the tail doesn't fizz; keep it low for a glassy, open space.
BREATH
How much the space moves — the depth of the breathing modulation.
0–100 % (default 25). Sets how deeply the slow 3-sine LFO modulates SIZE and character. At 0 the space is still; near 100 it inhales and exhales noticeably.
15–35 % keeps the tail alive without obvious wobble; go higher only for overt, evolving FX.
MIX
Dry/wet blend of the reverb.
0–100 % (default 35). Equal-power cross-fade, so there's no energy dip in the middle. At 100 % you hear only the wet space.
30–40 % is a natural insert blend; keep it at 100 % on a dedicated reverb send.
BREATH SYNC (FREE / SYNC)
Locks the breathing to your host tempo.
Toggle. FREE lets the breath run on its own slow organic rate; SYNC locks the breathing cycle to a musical DIVISION.
Turn SYNC on under rhythmic material so the space swells in time with the track instead of drifting against it.
DIVISION
The tempo-synced length of one breath cycle.
Choice: 1/2 · 1 bar · 2 bars · 4 bars (default 1 bar). Active when SYNC is on.
1 bar reads as obvious pulse; 2 or 4 bars give a long, slow swell that's easy to live in.
LOW CUT
High-pass on the whole plugin output.
0–100 % → 20–500 Hz (default 0 = OFF). Cuts lows from the full dry + wet output, so it's audible at any MIX, not just on the wet.
A touch of LOW CUT clears mud out of a big reverb so the low end of the mix stays defined.
HI CUT
Low-pass on the whole plugin output — the partner of LOW CUT.
0–100 % → 20 kHz–1.5 kHz (default 0 = OFF), inverted so more knob = darker. Rolls highs off the full output.
Use HI CUT for a vintage, behind-the-mix space without touching TONE inside the tail.
IN PHASE / mono-safe
Collapses the stereo image to a mono-compatible path.
Toggle. One click forces a positive phase correlation so the reverb doesn't cancel when summed to mono.
Leave it on when the track has to survive a club PA or a phone speaker.
IN / OUT
Input and output trim.
−24…+24 dB each (default 0). Stage gain into the engine and compensate level on the way out.
Trim IN down a touch on hot sources to keep the tail clean; use OUT to match bypass level when blending.
Tips & tricks
01
02
For an infinite pad, push DECAY to 100 % and play sustained chords; the tail freezes at the edge of unity and you can keep building on top of it.
03
Turn SYNC on and pick 2 bars under a slow track — the space breathes in time and feels composed rather than random.
04
Roll TONE up and add a little HI CUT for a dark, distant ambience that sits behind the mix instead of washing over it.
05
Use LOW CUT on bass-heavy material so the reverb stays wide and lush without clouding the low end.
06
Drag the CLOUD diagonally while it plays to audition SIZE and DECAY together — it's the fastest way to find the right room.
Troubleshooting
The tail rings with a metallic, resonant tone.
Raise SIZE a little and/or DECAY so the network stays dense — very small spaces with low decay have fewer echoes and can color. The FDN uses mutually-prime delays for density, but extreme settings expose the resonance.
The reverb sounds thin or hollow in mono.
Click IN PHASE / mono-safe. The wide stereo image uses phase relationships that partly cancel when summed to mono; IN PHASE forces a mono-compatible path so nothing drops out.
The breathing isn't locked to my beat.
Switch BREATH SYNC to SYNC and pick a DIVISION (e.g. 1 bar). In FREE the breath runs on its own organic rate and won't follow the host tempo.
My low end got muddy with a big reverb.
Bring up LOW CUT. It high-passes the full plugin output (dry + wet), so it cleans the lows even at low MIX — and pair it with TONE/HI CUT to darken the tail.
Specs
Formats: VST3 · AU
Systems: macOS (Apple Silicon)
Engine: FDN reverb (Householder matrix)
Tail: Up to infinite / freeze
Breath: Tempo-syncable, host BPM
License: AGPLv3 · open-source